diff --git a/src/Helper/Get-RandomKey.ps1 b/src/Helper/Get-RandomKey.ps1
index 206f400..907160a 100644
--- a/src/Helper/Get-RandomKey.ps1
+++ b/src/Helper/Get-RandomKey.ps1
@@ -32,6 +32,7 @@ function Get-RandomKey {
     [CmdletBinding()]
     param(
         [Parameter(Mandatory = $true)]
+        [ValidateNotNullOrEmpty()]
         [ValidateSet(16, 24, 32)]
         [string]$size
     )
diff --git a/tests/Helper/01_Get-RandomKey.Tests.ps1 b/tests/Helper/01_Get-RandomKey.Tests.ps1
new file mode 100644
index 0000000..f6ab645
--- /dev/null
+++ b/tests/Helper/01_Get-RandomKey.Tests.ps1
@@ -0,0 +1,39 @@
+#region HEADER
+$RepoRoot = (Get-GitDirectory).replace('\.git', '')
+$sut = (Split-Path -Leaf $MyInvocation.MyCommand.Path) -replace '\.Tests\.', '.'
+$sut = $sut -replace "\d{2}`_", ''
+$suthome = (Get-ChildItem -Path $RepoRoot -Exclude ".\tests\" -Filter $sut -Recurse).FullName
+# Skip try loading the source file if it doesn't exists.
+If ($suthome.Length -gt 0) {
+    . $suthome
+}
+Else {
+    Write-Warning ("Could not find source file {0}" -f $sut)
+}
+
+# load additional functions defined in the repository. Replace the expression <FunctionName>.
+# . (Get-ChildItem -Path $RepoRoot -Filter "<FunctionName>.ps1" -Recurse).FullName
+
+#endregion HEADER
+
+Describe "Get-RandomKey" {
+    Context "Basic input tests" {
+        It "Test1: Should throw if wrong size is given" {
+            {Get-RandomKey -size 43} | Should -Throw
+        }
+    }
+    Context "Basic syntax check" {
+        It "Test1: Should return a key with a length of 16" {
+            $Key = Get-RandomKey -size 16
+            $Key.length | Should -Be 16
+        }
+        It "Test2: Should return a key with a length of 24" {
+            $Key = Get-RandomKey -size 24
+            $Key.length | Should -Be 24
+        }
+        It "Test3: Should return a key with a length of 32" {
+            $Key = Get-RandomKey -size 32
+            $Key.length | Should -Be 32
+        }
+    }
+}